In some internal combustion engine applications, liquid propane injection can provide some potential benefits relative to gaseous propane injection in ether port fuel injection or direct fuel injection systems. As one example, liquid propane injection provides reduced air displacement that allows for increased air mass to enter an engine cylinder resulting in increased volumetric efficiency relative to gaseous propane injection. As another example, liquid propane injection provides increased charge cooling in an engine cylinder relative to gaseous propane injection.
A typical liquid injection propane fuel system for an internal combustion engine supplies liquid propane from a pressurized tank via a fuel pump to a fuel rail. The liquid propane is injected from the fuel rail to cylinders of the internal combustion engine via fuel injectors. Excess fuel can be returned to the pressurized tank during operation via a pressure relief supply line.
However, the inventor has recognized several potential issues with such liquid propane fuel systems. For example, during engine shut-off conditions, fuel rail pressure is reduced so that propane cannot be pumped back to the fuel tank via the pressure relief supply line and instead resides in the fuel rail. The liquid propane residing in the fuel rail during engine shut-off conditions may evaporate and leak out of the fuel rail via the fuel injectors into the atmosphere causing increased emissions and reduced fuel economy.
In one example, the above mentioned issues may be addressed by a method for controlling fuel flow in a vehicle. The method may comprise during a first mode of operation, directing fuel pumped by a fuel pump from a fuel tank to a fuel rail for injection to an engine, and during a second mode of operation, directing fuel pumped by the fuel pump to an ejector to provide a motive flow for the ejector to pump fuel from the fuel rail to the fuel tank.
As an example, the first mode may be performed during a vehicle in-use condition and the second mode may be performed during a vehicle shut-off condition. By implementing an ejector in communication with the fuel pump to evacuate fuel from the fuel rail back to the fuel tank, fuel residing in the fuel rail during the vehicle shut-off condition can be reduced. In this way, evaporative emissions resulting from fuel in the fuel rail evaporating and leaking out of the fuel injectors can be reduced and fuel economy can be increased.
Furthermore, since a fuel pump that already exists in the fuel delivery system provides the motive flow for the ejector, no additional pump sources (e.g., mechanical vacuum pump, compressor, etc.) are needed to evacuate the fuel rail (although additional pumps may be used, if desired). In this way, fuel rail evacuation may be performed with reduced expense relative to a system that implements additional pump sources. Furthermore, since the ejector has no moving parts or mechanical pumps, the ejector is able to evacuate fuel from the fuel rail back to the fuel tank even if the fuel changes phase between a liquid state and a gaseous state, which may be especially beneficial in liquid injection propane fuel system applications.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this description.